Successful human islet transplants have demonstrated the potential of islet cell replacement therapies in type 1 diabetes. Preclinical proof-of-concept studies showing prolonged diabetes reversal after porcine islet transplantation in monkeys suggest that xenografts could provide the unlimited supply of islets required for cell replacement therapies to become widely available and impactful in diabetes care. However, critical reviews of the field conclude that the immune response to islet xenografts is vigorous and that a consistently effective and clinically applicable regimen for preventing islet xenograft rejection is not yet available. Thus, the single most significant remaining barrier to unlocking th profound potential of pig islet transplantation is the immunity to islet xenografts. Our data indicates that intraportal porcine islet xenografts in cynomolgus monkeys (CM) activate T cells with both direct and indirect specificity. It is also becoming increasingly apparent that B cells ae instrumental in priming the T cell response to islet xenografts and potentially enhancing the effector functions of graft-infiltrating T cells. We hypothesize that drug-free pig-to-CM islet xenograft survival can be prolonged with a rejection prophylaxis that i) blocks B cells to prime xenogeneic T cell responses and memory generation, ii) deletes anti-donor T cells with indirect specificity and expands regulatory B and T cells, and iii) deletes direct pathway MHC class I-restricted anti-donor CD8+ T cells or interferes with their activation and effector function. To tet this hypothesis, we will pursue three AIMS: Aim #1: To clonally produce genetically modified pigs for use in islet xenotransplantation in CM. AIM #2: To examine the efficacy of antigen-specific immunotherapies and genetically modified adult pig islets in prolonging drug-free islet xenograft survival in CM given transient immunosuppression. AIM #3: To determine the effects of the immunotherapeutic protocol on mechanisms underlying the induction, maintenance, and/or loss of donor-specific unresponsiveness to islet xenografts in CM. The proposed studies will provide important insights into the efficacy and mechanisms of novel xenoantigen-specific cellular immunotherapeutics and B cell-targeting therapies in genetically modifies porcine donor-to-nonhuman primate islet xenotransplantation.